This invention relates to a system for controlling original image scanning for use in a slit exposure type image recording apparatus and, more particularly, to a system for controlling an original image scanning for use in a slit exposure type copying machine or printer with provision for a movable original image and a fixed optical system or for a fixed original image and a movable optical system.
In such a type of copying machine or printer, there is provided a variable magnification device for adjusting the magnification or enlargement of an entire copy image relative to the original image by varying the focal length of the lens of the optical system or the total optical path length thereof, thereby providing a different enlargement of the copy image. In this case, and dependent upon the setting of the magnification ratio, it will be necessary to adjust the magnification in the direction of forwarding the copy image relative to its original image or the longitudinal magnification by varying the rate of movement of the original image or optical system during the original image projection (such movement being herein referred to as original image scanning). Especially in a printer using a microfilm of 35 mm size, it is fundamental to use a microfilm image having a reduction of 1/15 in size as an original image and produce a copy image of practical size magnified or enlarged by 15 times from the original image. It is, however, desired that the same original image be enlarged by 101/2 times and then copied on paper having a size 1/2 smaller than the full scale size of paper. For example, an original drawing of A2-size is reduced to provide a copy image of A3-size. It is further required that since there are used various types of microfilms having different ratios of image reduction and apparatus for producing microfilms would have differences up to about several percent in their reduction in size, the magnification of the printers needs to be finely adjusted to compensate for the differences and errors in the ratio of reduction, thereby producing the desired size of copy images.
In this case, the magnification in the direction of the image scanning (hereinafter referred to as longitudinal magnification) is given by dividing by the original scanning speed the surface speed of an image recording material or photosensitive material on which the original image is projected to form a copy image thereon. In ordinary printers in each of which the photosensitive material is moved at a predetermined speed, the original scanning speed is adjusted to vary the longitudinal magnification in order to satisfy the above-mentioned requirements. In conventional printers, however, it has been impossible to satisfy such requirements, because each of the printers is arranged such that a cylindrical drum having the photosensitive material on its surface is rotated at a predetermined speed and its rotational motion is converted to a linear motion through, for example, a pulley transmission device and a belt to achieve the original scanning and thus the original scanning speed or longitudinal magnification corresponding to the transmission step of the transmission device can only be selected.
Furthermore, the microfilm is taken such that the center of the original image is positioned at the center of the photographed portion of the film irrespective of the size of the original image and thus it is necessary to vary the initial position of the original image scanning dependent upon the size of the original image. Thus, there is a drawback that the device for this purpose is complicated in construction.